Restriction of analysis at toxic waste sites to analytical chemistry is incomplete since results do not yield indication of the biological significance of contaminants present. A toxicity-based approach to characterization of sites, prioritization of locales within a site, and monitoring of bioremediation is warranted. This approach directs chemical analysis and subsequent identification to only those fractions proven toxic. Toxicity assays would need to encompass a variety of relevant end- point (mutagenicity, carcinogenicity, and embryos and developmental toxicity). Fish provide potentially important nonmammalian, vertebrate models for special applications in toxicity evaluation. The medaka (Oryzias latipes), a small aquarium fish, provides economy and speed of assay. Large numbers may be cultured in a small space, small body size permits histopathologic sampling of all organs, and serial section analysis in target organs enables complete sampling for morphologic assessment. Medaka have transparent chorions enabling noninvasive assessment of development. Using microinjection test agent is presented at a time during which rapid growth of tissues assures "fixation" of genotoxic adducts. Hatchlings are sensitive and easily adapted for 73 hr toxicity screens of aqueous extracts, leachate, and particulate emissions. Medaka develop tumors rapidly. Our development and use of a purified diet for medaka further improves precision of chronic bioassays. An aquatic toxicologist and an applied toxicologist will team to apply a toxicity-based approach to initial characterization of toxic waste sites, identification of toxicants in complex mixtures and detection of toxicity associated with leachate and emissions from hazardous wastes. The following specific aims are proposed: I) establish toxicity based-characteristics of hazardous waste sites providing a rational basis for prioritization and monitoring of bioremediation efforts, II) decrease time and cost of toxic chemical contaminant identification in complex mixtures, III) determine the toxicity, in a novel embryo microinjection test of airborne pollutants as potential aquatic contaminants, and IV) determine the metabolism of and the biological consequence(s) associated with exposure to model organic compounds of demonstrated potential for leaching to groundwater.